For example, components of turbines are nowadays quite often made of materials with an oriented microstructure. Particularly monocrystalline materials and materials that have a grain structure, the extent of the grains having a common preferential direction, are to be regarded here as materials with an oriented microstructure. For example, the grains may have a larger dimension in a particular preferential direction than in the other directions. Components with such a grain structure are also referred to as directionally solidified components.
Strongly loaded components, for instance turbine blades, are subjected to heavy thermal and mechanical stresses during operation, which can lead to material fatigue and therefore cracks. Since it is relatively expensive to produce components from base materials that have an oriented microstructure, it is generally necessary to repair such components after the onset of damage. This restores the ability to operate and the component can be used for a further revision period.
Soldering, for example, is one way of repairing damaged components. For such soldering, a solder is applied onto the material of the component in the region of the damage, i.e. onto the base material, and bonded to the base material by means of a heating effect. With the hitherto conventional procedure, however, the solder material does not have a monocrystalline or directionally solidified structure after soldering. Compared to an oriented microstructure, moreover, an unordered structure has poorer material properties—especially in the high temperature range—so that the solder site has inferior material properties than the surrounding base material.
Welding methods, by which oriented microstructures can also be generated in the welded structures, are also available for repairing damaged components with an oriented microstructure. Such a method is disclosed, for example, in EP 089 090 A1.
Other methods or usable solder powders are known from the publications U.S. Pat. Nos. 6,283,356, 4,705,203, 4,900,394, 6,565,678, 4,830,934, 4,878,953, 5,666,643, 6,454,885, 6,503,349, 5,523,170, 4,878,953, 4,987,736, 5,806,751, 5,783,318, 5,873,703.
U.S. Pat. No. 6,050,477 discloses a method for bonding two component elements, the solder being applied over a large area between the two component parts and a temperature gradient being used in order to generate the same oriented microstructure.
US-A 2003/0075587 A1 discloses a method for repairing a component with a directionally solidified microstructure, although the site to be repaired does not have the same microstructure as the component to be repaired.
U.S. Pat. No. 6,495,793 discloses a repair method for nickel-based superalloys in which a laser is used, the laser melting the material which is supplied via a material feeder. Information about the microstructure of the component or the repair site is not given.
EP 1 258 545 A1 discloses a soldering method without temperature gradients.
EP 1 340 567 A1 discloses a method in which additional material is supplied to the pre-melted site to be repaired. A temperature gradient is likewise used in order to treat the components with an oriented microstructure.
U.S. Pat. No. 4,878,953 discloses a method for repairing a component with an oriented microstructure, in which material is applied onto the repair site by means of powder and this site has a fine-grained microstructure.
Welding methods, however, melt the base material of the component to be repaired. Structurally supporting regions of a component should therefore not be welded, since melting the base material would cause the integrity of the oriented structure to be lost. Components with an oriented microstructure are therefore repaired by means of welding methods only when the damage does not lie in structurally supporting regions of the component. When the damage lies in a structurally supporting region of the component and if an oriented weld structure is required, however, then this component is declared irreparable and replaced with an intact component.